Refrigeration Cycle Flashcards
Describe the purpose of Chillers
-They use Freon/refrigerant to cool liquid in the AHU’s that maintain temperature in rooms for equip. and personnel.
Describe the refrigeration cycle
-Compression using compressor
-Condensation using condenser
-Expansion in the Flash economizer
-Evaporator using the cooler
Describe compressor surge
-Reversal of flow from the condenser to the cooler
-Back flow of refrigerant through the compressor due to higher D/P than the compressor can produce.
-30psi in the condenser and the compressor produces 29psi, back flow will occur
-Hot gas bypass prevents it
Describe Refrigerant stacking
-Prevention of flow to the cooler due to too low of D/P in the system
-Differential pressure is the motive force after the compressor so if there is no difference then flow stops
-Prevented by RHCV which controls cooling water flow which controls condenser pressure
Describe the purpose and operation of PVGS Chiller inlet guide vanes
-The PURPOSE is to control the flow of Freon vapor leaving the cooler and going to the compressor.
-The OPERATION is they open and close in response to the temperature of chilled water LEAVING the cooler
Describe the purpose and operation of PVGS chillers compressor
Purpose:
To raise the temperature or the refrigerant above the condenser cooling water
Operation:
-2 stage compressor driven by 4.16kv motor.
-first stage draws low psi, high temp freon
-second stage increases psi and temp. along with flash gas
Describe the purpose and operation of chillers condenser
Purpose:
-Condenser rejects heat picked up by freon in the cooler from the chilled water and sends the heat to the cooling water system
Operation:
-2 pass shell and tube HX
-refrigerant on the shell side
-cooling water on the tube side
-condenses Freon vapor entering the condenser
What’s Thermal Economizer
-Bottom 12% of condenser
-Separated from the top of the condenser with holes at the ends
- Used to subcool the freon to increase efficiency
-Liquid from here goes to the flash gas chamber via the high side float valve
Describe purpose and operation of the Flash economizer
Purpose:
-Provides a pressure boundary/barrier between the condenser and cooler
-This regulates the freon flow from the condenser to the cooler
Operation:
Consist of:
-High side float valve
(controls condenser lvl)
-low side float valve
(allows Freon to go to the cooler, maintain D/P)
-flash gas chamber (expanded volume causes low pressure)
And -main chamber
Describe the purpose and operation of PVGS chillers cooler
Purpose:
-Purpose is to transfer heat from the chilled water used to cool HVAC to the refrigerant
Operation:
-2 pass shell and tube HX
-Low psi and low temp absorbs heat from the chilled water coming from the HVAC
Describe the purpose and operation of PVGS chiller pump down unit
Purpose:
-Used to transfer Freon to and from the storage tanks below the chilller, as necessary for maintenance
Operation:
Consist of:
-pump down comp. And motor
-condenser
-storage tanks(x2)
-piping and valves
-Controlled by HVAC personnel
What are the corresponding components of a chiller?
-Compressor
-Condenser
-Flash economizer
-Cooler
What cools the compressor?
-Liquid refrigerant from a sump in the bottom of the condenser
-The D/P between the condenser and cooler maintains flow
What lubricates the compressor bearings?
-Oil from a reservoir in the base of the compressor is pumped through a cooler and filter to the bearings
What controls the oil temp when shutdown?
-Immersed heaters in the oil sump
